When to photograph M 39
M 39 is an open cluster in Cygnus, 20′ across at magnitude 4.6. Also listed as NGC 7092.
When to photograph it
From 45° N the best months are September and October, with up to 8.0 hours of astronomical darkness above 30° in September. It reaches 87° at its highest. It never sets from this latitude, so some imaging is possible all year.
From 35° S it never climbs above 30°. It peaks at 7° when it crosses the meridian, low enough that haze and light pollution soften it. It is possible with a clear northern horizon, but hard.
Framing
Its long axis is 20′. It fills 35 to 80% of the short side of an APS-C sensor at about 960 to 2200 mm, and of a full-frame sensor at about 1480 to 3380 mm.
Filters and the moon
Clusters are broadband targets, but bright ones tolerate some moonlight and light pollution. Short subs keep the brightest stars from clipping. The dark sky calendar shows which nights this month are moon-free where you are.
Plan it for tonight
Dates and times depend on your exact location. The imaging planner shows M 39's altitude through tonight, its transit time and its distance from the moon. For sub length, use the exposure calculator.
Nearby targets
- IC 5146 Cocoon Nebula 3.8° away
- NGC 7000 North America Nebula 6.8° away
- NGC 7243 7.2° away
- IC 5070 Pelican Nebula 8.1° away
- IC 1396 Elephant's Trunk Nebula 9.1° away
- NGC 6914 13.1° away
Gear that suits M 39
M 39 is 20′ along its long axis. These frame it on an APS-C sensor with room to crop.
- Celestron C8 OTA 2032 mm f/10: fills 74% of an APS-C frame's short side View at High Point Scientific
- Celestron EdgeHD 8 OTA 2032 mm f/10: fills 74% of an APS-C frame's short side View at High Point Scientific
- Sky-Watcher Esprit 120ED 840 mm f/7: fills 31% of an APS-C frame's short side View at High Point Scientific
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